i learned a lot about fake and authentic denim on honestforum, which i've ben a member of a little over 2 years... brands like rock & republic, true religion, citizens, sfam are popular there
it's kinda like PF, but for denim... ever since i've been on pf, though, i don't visit HF as much. i don't buy denim off ebay anymore, although, you can find great deals on authentic jeans.